Pickling



Patented Feb. 9, 1926.

' UNITED STATES PATENT OFFICE.

HENRY S. MARSH AND HALF S. COCHRAN, OF YOUNGSTOWN, OHIO, ASSIGNORS TODELAWARE.

No Drawing.

To all whom it may concern:

Be it known that we, HENRY S. Mlansu and RALF S. CooHRAN, residing atYoungstown, in the county of Mahoning and State of Ohio, both citizensof the United States, have invented or discovered certain ,new anduseful Improvements in Pickling, of which improvements the following isa specification. f

Our invention relates to improvements in the method of pickling ferrousarticles, particularly rolled steel sheets and plates, and its objectsare the production of clean surfaces, and also the overcoming of ditionswhich tend to delay and prolong the normal operation of pickling.

In the practice of pickling rolled steel sheets and plates, the articlesare apt [to come from the pickling vat, not bright and white, as theyshould be, but clouded and mottled and streaked with dull brown. A sheetor plate so discolored is, because of its very appearance, lessacceptable to the customer, and, furthermore, it is in some respectsinferior in utility and serviceability. For instance, the scrap cut fromthe sheets or plates in their further fabrication, is commonly fashionedto other articles. The articles so produced are sometimes found to bedefective, in that they are not responsive to the case-hardeningoperation.

\l/Ve have investigated, and have discovered that the mottled anddarkened appearance upon the surfaces of the sheets and plates, is dueto the presence of other metals, chiefly copper, and, in less degree,arsenic and lead, electroplated upon or otherwise oleposited upon thesteel surfaces while in the picklingbath.

Copper has of late years been increasing- 1y used as an alloy of iron,and this, together with the circumstances that steel parts are inindustry enerally, often provided with copper fittings of one sort andanother, results in this: that steel scrap contains a very appreciable,though very un-- certain, copper content. In steel-making steel'scrap'is charged together with pig iron into the refining furnace, andin consequence copper appears as an appreciable ingredient of the newlyproduced steel. In the preparation of the pickling bath, too, and in thereclaiming of spent pickling so+ lutions, the dilute acid whichconstitutes BICKLING.

I Application filed November 14, 1924. Serial No. 749,981.

operation is performed upon steel sheets and plates, two undeslrablecircumstances appear: first, the sheets and plates are apt to come fromthe bath mottled and dirty in appearance, as has been said. This weimpute primarily to the presence of cop per, and in less degree to leadand arsenlc. In the second place, the operation of pickling is retarded,and this we impute primarily to the -presence of lead and arsenic,

which act as inhibitors, and in less degree to copper.

The pickling solution, attacking the surface of the sheet, tends to eataway the cop-' per as well as the iron, but there is a countervailingtendency of the copper salt in solution sulphate, ordinarily) (c ppOHIO, A CORPORATION OF whether initially present in the bath, or

derived from thematerial under treatment, to break up; the phenomenon ofelectrolysis appears, and metallic copper is deposited' electrolyticallyupon the surface of the steel sheet or plate. The dull and dirtyappearance of this deposit is due to the condition of the electrolyte,and particularly to the presence of other metals or metalloids,deposited with the copper."

We have discovered, and herein lies our invention, that by generating inthe pickling bath and in sufficient quantities, sulphu- -rettedhydrogen, the copper present in the nated, the electrolytic depositswill not occur, nor will the normal pickling operation be retarded.

In the practice of our invention we preferably begin with the picklingliquid reclaimed from previous service. We bring" this pickling liquidinto a suitable tank or container, where we introduce into it ironsulphide. The acid reacts upon the iron gen; the sulphuretted hydrogenreacts upon the salts of the undesired etals and forms separation byincreasing the temperature of the liquid to approximately120 F. vAndthis We conveniently-acc0mplish by the injection of s'team'into theliquid.

' 'Pro'ce'eding to the pickling operation itself, we introduce ironsulphide into the pickling vat also. And there also the acid reactingupon the iron sulphide releases sub phuretted hydrogen; And thesulphuretted hydrogen in turn, reacting with the copper as it is eatenby the acid from the sheets or plates under treatment, forms coppersulphide, and in that ultimate form the copper a the bath with thedesired 1 is eliminated from the further reactions, and.

held from electrolytic deposition. Similarly there is no deposit ofother undesired metal, and the sheets and plates go from bright andclean surfaces.

In order to make our invention elfective to the fullestextent, it isdesirable that the pickling bath be at all times saturated withsulphuretted hydrogen. This is a condition which in practice is notdiificult to main- I tain; all'that'is requisite is that the iron;

sulphide be supplied in such quantity that the bath smells ofsulphuretted hydrogen.

The relatively high temperature normally maintained in pickling tends ofcourse to re lease whatever sulphuretted hydrogen may be present insolution. In, order therefore to insure the presence of the sulphurettedhydrogen in suflicient quantities, we maintain within the pickling vatgood-sized I lumps of iron sulphide. From. these the sulphurettedhydrogen is enerated gradually, and as itis generated it is taken upfound the difiiculty less, to the correction of which our invention isaddressed. But in the case of heavier sheets and plates, and 1n case thecoatings of oxide are continuous and heavy, we are able in the practiceof our invention to overcome a difiiculty'of sub-- stantial magnitudeand achieve a substantial gain. i

. lVe claim' as our invention 1. The method herein described oi picklingmetallic objects which consists in con-' ducting the pickling operationin a pickling solution burdened with sulphuretted hydrogen.

2. The method herein described of producing bright-surfaced pickledarticlesof adulterated iron which consists in conducting the picklingvoperation in a pickling bath saturated with sulphuretted hydrogen.

3. The method herein described of conducting the pickling operation uponmetallicobJects which consists in causing reclaimed pickling solution atelevated temperature to react upon iron sulphide, allowing theprecipitate to settle, and introducing the articles to' be pickled intothe solution so previously treated.

4. A pickling bath consisting of a body of dilutesulphuric acid, havingimmersed in it lumps of iron sulphide.

In testimony whereof we have hereunto set our hands.

HENRY s. MAR-SH- RALF s. COCHRAN.

